Carbohydrates are excellent starting materials for the production of bulk and specialty chemicals. Intelligent usage of the intrinsic functionality is already present in carbohydrates. Furan chemicals (for example, 2-hydroxymethyl furan (HMF)) are known to have high potential as a starting material for industry.
Furan carboxylates, such as 2,5-furandicarboxylic acid (FDCA), have been traditionally used e.g. in pharmacology, where its diethyl ester has showed a strong anesthetic activity. FDCA is also a very powerful chelating agent. In medicine, it is e.g. used to treat kidney stones, but also in the preparation of grafts having biological properties similar to those of natural tissues, and which are characterized by a lack of rejection after transplantation.
FDCA has also been used as a basic monomer in the manufacture of polymers such as polyesters, polyamides, co-polymers or polyurethanes, e.g. for improving their mechanical properties. In polyesters, it is likely to be used in replacement of phthalates. In view of such a possibility, the FDCA has been ranked among the 12 raw materials with the greatest industrial potential (Werpy and Peterson, 2004).
Furan carboxylates are also realistic alternative to terephthalic acid, which is a monomer used in polyethylene terephthalate production and used for example in plastic bottles. The bio-based furan carboxylate solution should therefore be both chemically efficient and environmentally sustainable.
Monocarboxylates such as 2-furoic acid finds uses as a monomer, preservative, flavouring agent, and it may have use in optic technologies. The 2-furoic acid esters can be used for example as bio-based fuel components.
Traditionally furan carboxylates are prepared using either unstable intermediates (HMF) or from aldaric acids by using excess strong mineral acids. Both of these routes limit the scalability of the process and produce highly toxic waste, which is damaging to the environment.
There are currently two main routes to furan carboxylates. First route is through synthesis of HMF and transformation to furan carboxylate. This process is limited on scale because of the instability of the intermediate. Many methods exist but are hampered by this limiting factor. Second route is through aldaric acids via use of strong mineral acids. There are two main problems with this route, firstly the yields are limited to around 60% and secondly the acidic reaction solvent cannot be recycled and is highly toxic to the environment.
French patent FR 2723945 (1996) describes furan synthesis from galactaric acid with and excess of strong mineral acids (HBr, HCl, H2SO4, H2NO4, H2PO4). Yields vary between 35 to 66%, but the reaction time is long (9 to 10 hours) and the method produces toxic waste.
Furan carboxylates have promising industrial potential. However, their traditional synthesis methods have several drawbacks, such as operating under relative severe conditions, generating large amounts of toxic waste and resulting poor yields. Thus, there is a need for a sustainable, quick and easily up-scalable production process for furan (mono- and di-) carboxylates.